Making zinc pigment



Patented Sept. 27, 1938 2,131,313

UNITED TATES PATENT. OFFICE."

I No Drawing. Application May 24, 1937,

Serial No. 144,562

10 Claims. (01. 23-435) This invention relates to making zinc pigments; with precipitation of the zinc as oxy-carbonate and it comprises an improvement in processes by boiling the liquor, it is found in practice that of recovering zinc in pigmentary form from sal the oxy-carbonatecarries enough chloride to be skimmings and crude impure zinciferous mateobjectionable. And the presence of manganese, 7 h

rials generally by extraction withammoniacalwhich often occurs, is also harmful.

carbonate solutions wherein the ammoniacal In a prior and copendin app Serial solution at one stage in the operation is treated No. 92,235, I have described and claimed a cyclic with a phosphate to precipitate manganese as p ss of ec ve e Values o W in ammonium manganese phosphate insoluble in e spect t e present invention is an 10 the ammoniacal liquid; and more specifically it prevement. n the proeess'of e'prior applica- 10 relates to a process of recovering zinc sulfide in n Waste skimmings containi chlorides are a state of sufficient purity for pigmentary purextracted with ammoniacal ammonium carbonate poses wherein the sal skimmings are first exsolution in the presence of suflicient lime to react tracted by ammoniacal a m ni m arb t with the chlorides and form calcium chloride.

solution including recycled liquor, in the presence After separation insoluble impurities, the 15;

of some lime, the liquid is separated fro t tract liquor is boiled to drive off CO2 and aminsoluble bodies, is boiled to precipitate zinc moiiia, Which are recovered, With seperatieh 0f 7 oXy-carbonate with recovery of ammonia and ex- Zinev a at The y-oa is pcess CO2, the precipitate is separated from a d. t e mother qu r carrying s d e 2o mother liquor containing chlorides and other imsoluble impurity being di a d. The pr p purities, is redissolved in ammoniacal ammonium tete is e so ved in ammoniacal ammonium carcarbonate solution, alittle phosphate added to the honate solution, giving a further separation of solution to precipitate manganese and zinc is reinseiilbies which go out Of the y The new covered as a substantially chlorine-free and man Solution is boiled to re-piecipitete vZine Y- ganese-free zinc sulfide by addition of a soluble bonate W i is filtered f or. otherwise sepa- 25- sulfide, best ammonium sulfide or hydrogen sulrated, the mother liquor being recycled; b g fide, the mother liquid b in recycled for use in added to the ammoniacal solution used in exthe first stated operation; all as more fully heretracting further quantities 0 the sal skimmingsinafter set forth and as l i d This cyclic process represents certain economies In the recovery of zinc from wa t material, in heat and materials, and has the further out- 30; such as the waste materials produced in the gal- Standing advantage in t the exit-Carbonate vanizing industry d known galvanizers, recovered in the second precipitation issubstanwaste, sal skimmings, dry skimming s, zinc ashe tially pure, being in particular practically free of etc., and from crude zinciferous materials genera chioiine- It is useful in making e p s ally, one of the many methods that have been and other ep p a e s- 35 used is the extraction of the material "with an It is how my discovery that in such a process ammoniacal l ti of ammonium at the operation is facilitated and purer products Such a solution is advantageous as an extraction Obtained y adding a small q y of a Soluble agent because of its power of dissolving zinc oxide sphate, such as ammonium p p e 0 o- 40 while leaving undissolved various impurities, such dium phosphate, t0 the ammoniacai Zinc. l as alumin nd iron d Silica and compounds tion, advantageously the second solution: that of the various heavy metals (Fe, 'Ni, Cu, Mn, etc.) resulting from the Solution of the first oXy-car- There is often somelittle diificulty in Securing a bonate precipitate. In particular, this addition wholly complete separation of the heavy metals serves o precipitate themangenese in the form in this operation. Traces of other metals than of a P p e inso u le in the ammoniacal 45 zinc going forward may impair pigmentary values q Most manganous p ds are more O considerably. This is particularly true as reless soluble in an excess of ammonium carbonate gards manganese compounds which tend to disbut ammonium manganese phosphate is an coloration in air. g ception. The fact is utilized in the present in- Extreme purity, at least as regards certain for- V i n- 50. eign bodies, is required in a good and permanent By filtering out the manganese precipitate,

zinc pigment. For some reason, even the pres-- the second zinc precipitation from the ammonience of chlorides in such a pigment is harmful. acal carbonate solution gives a material which In the use of ammoniacal ammonium carbon is not only chlorine-free but also manganese free.

: ate solution for extracting sal skimmings, etc. This removal of manganese is useful in the proc- 55? ess of the prior application where there is a double precipitation of oxy-carbonate but it is now also useful in modified processes where the redissolved oxy-carbonate of the first precipitation is converted into pigmentary Zinc sulfide by an addition of a soluble sulfide. In so doing, any soluble sulfide may be employed as a precipitant. If barium sulfide be used, the zinc sulfide then carries barium carbonate which has pigmentary value.

In practice of the cyclic process, the first stage or extraction-digestion of the crude material in ammoniacal ammonium carbonatesolution with addition of lime efiects a substantially complete solution of the zinc oxide compounds in the material treated. Filtration separates insoluble impurities existing as heavy metal compounds together with silica and alumina and excess lime. The subsequent boiling of the filtrate with precipitation of zinc oxy-carbonate and recovery of the ammonia and excess CO2 leaves nearly all of the soluble chlorides and other soluble impurities in solution which is discarded. The precipitated zinc oxy-carbonate has only a small content of chloride. The re-solution of this precipitate in ammoniacal carbonate gives a further separation of insoluble impurities and any zinc which remains insoluble in the re-solution step is recovered by the return of the insoluble matter to be extracted in the first digestion step. As I have found, manganese if present has a tendency to accompany thezinc in the several extraction and precipitation steps. But I find that a selective precipitation of manganese and separation from the zinc is efiected by the addition of a small amount of ammonium or sodium phosphate to the circulating liquid system. The complex ammonium manganese phosphate is, advantageously, precipitated by the phosphate addition with the insoluble impurities remaining from. the re-solution of the first precipitate in ammoniacal carbonate. However, if desired, it may be precipitated and removed separately. The second oxy-carbonate of zinc solution, upon addition thereto of ammonium or sodium sulfide, yields a pure white zinc sulfide precipitate substantially chloride-free and also free of heavy metal compounds. The process is operated to insure a substantially complete separation of iron in the ferric form as insoluble compounds; the phosphate addition aiding in this separation. In the final precipitation of zinc sulfide from the purified filtrate derived from the second extraction by ammoniacal carbonate, it is unnecessary to effeet a wholly complete precipitation of the zinc content of the solution. Any zinc remaining in the mother liquor after precipitation is returned to the first digestion or extraction step of the process and is recovered. The soluble impurities in this mother liquor, including salts of metals resulting from the sulfide precipitation, are also returned to the digestion and are discarded with the filtrate obtained after the first precipitation of zinc oxy-carbonate. In the process the insoluble impurities are separated and discarded in the first extraction and the soluble impurities, particularly chlorides, arediscarded inthe filtrate liquor remaining after the first precipitation.

I find that the addition to the cyclic system of smal lamounts of soluble phosphate aids materially in the purification of the zinc product. When the soluble phosphate is added to the second ammoniacal carbonate extract prior to the second precipitation of zinc either as .oxy-car bonate or as sulfide, I have found that it is often not necessary to filter ofi' the ammonium manganese phosphate precipitate. This white substance may be allowed to remain with the zinc precipitate without adverse discoloration effect. In practice however it is usually advantageous to add phosphate during the second extraction step and to separate insoluble phosphate precipitate from the ammoniacal carbonate zinc solution. The second; precipitation'step of the cyclic'process in which the zinc is precipitated as zinc sulfide yields a product of unusual purity and stability. as a pigment.

As amethod of making zinc sulfide from crude zinc raw materials generally, the process of extracting the-oxide in an ammoniacal carbonate solution and precipitating zinc sulfide from such a solution has great economic advantage over prior processes in which zinc salts of strong mineral acids such as the sulfate are treated in solution with sulfides and quantities of by-product salts formed in the reaction have to be disposed of. By using ammonium sulfide or hydrogen sulfide as the zinc precipitant in the present process, ammonia and ammonium carbonateare recovered and cyclically reused. Whensodium sulfide is the precipitant, soda; is removed with the solubles by return of the liquid for. cyclic use in extracting zinc crudes; V

The separation effected between zinc and manganese in ammoniacal carbonate solution by addition of phosphate isa valuable feature in the extraction of crude materials generally.

What I claim is l. A process of making zinc sulfide for pigments .from crude zinc materials, which comprises extracting the material with a solution of ammonium carbonate and ammonia, boiling the solution extract to precipitate zinc oxy-carbonate, redissolving the precipitate in ammoniacal, ammonium carbonate" solution with addition of a soluble phosphate and precipitating zinc sulfide from said solution by addition :of a soluble sulfide. V

2. A process of converting chloride-containing zinc compoundsintoa substantially chloride-free zinc sulfide which comprises treating the chloride compound with anammoniacal ammonium carbonate solution withaddition oflime to dissolve zinc compounds, discarding insoluble matter, boiling the solution to precipitate zinc oXy-carbonate separatingfthe pre'cipitatewith-discard of soluble matter and redissolving it in ammoniated ammonium carbonate solution with separation of insoluble matter and precipitating zinc sulfide from this solution byaddition'thereto of a soluble sulfide. v:

3. In a process ofrecovering zinc compounds from crude zincifer'ous materials containing manganese compounds wherein zinc compounds are first extracted by an ammoniacal solution, precipitated by boiling the solution extract, re-extracted in an ammoniacal solutioniand reprecipitated, the improvement which comprises adding a soluble phosphate to thesecondammo niacal zinc solution.

4. In obtaining 'from' impure chloride-containingzinciferous material-substantially pure zinc sulfide, a cyclic process which comprises extracting the material with ammoniacal ammonium carbonate solution with an addition of lime converting chlorides of'the material to calcium chloride and with discard ofinsoluble matter, boiling the extract to recover ammonia and to precipitate zinc oxy-carbonata discarding chloride-containing liquor, redissolving the precipitate in ammoniacal ammonium carbonate solution with separation and recycling of insoluble matter, adding to this second solution a soluble sulfide to precipitate substantially pure zinc sulfide and recycling the liquor from the precipitation to the first ammoniacal extraction of impure materials.

5. In the process of claim 4, adding a soluble phosphate to the re-soluticn of zinc oxycarbonate in ammoniacal ammonium carbonate solution.

6. In the recovery of zinc from zinciferous materials as commercial pigments the process of obviating the effects of manganese compounds when present which comprises adding a small amount of phosphate to an ammoniacal solution of zinc, the amount being about that suificient to precipitate the manganese present.

7. In the process of claim 6, removing the manganese precipitate and converting the zinc into zinc sulfide.

8. In a cyclic process of recovering zinc values from impure materials by a double extraction in ammoniacal carbonate solution and reprecipitation with discard of insoluble impurities at one point in the cycle and of dissolved impurities at another point, the improvement which comprises adding a soluble phosphate to one of said ammoniacal carbonate solution extracts to aid in removal of the insoluble impurities and recovering pigment zinc sulfide by adding a soluble sulfide for the reprecipitation from the second ammoniacal carbonate extract.

9. In processes of extracting zinc values from crude manganiferous materials with extraction by an aqueous ammoniacal carbonate solution, the improvement in recovering a pure zinc product Which comprises adding a soluble phosphate to said zinc solution in about the amount required to precipitate the manganese and removing the insoluble manganese ammonium phosphate thereby formed.

10. In the process of claim 2, precipitating zinc sulfide from the second ammoniacal ammonium carbonate solution by addition thereto of ammonium sulfide.

HENRY SEYMOUR ooL'ro 

